"regions = pd.DataFrame({'RegionID': ['NSW1','QLD1','SA1','VIC1','TAS1']})\ndate1 = pd.DataFrame({'Date1': regional_df.Publish_Datetime.unique()})\ndate2 = pd.DataFrame({'Date2': regional_df.Publish_Datetime.unique()})\n\n# define selection dropdowns\nregion_dropdown = alt.binding_select(options=list(regions.RegionID))\nregion_selection = alt.selection_single(bind=region_dropdown, fields=['RegionID'], name='Region_')\n\ndate1_dropdown = alt.binding_select(options=list(date1.Date1))\ndate1_selection = alt.selection_single(bind=date1_dropdown, fields=['Publish_Datetime'])\n\ndate2_dropdown = alt.binding_select(options=list(date2.Date2))\ndate2_selection = alt.selection_single(bind=date2_dropdown, fields=['Publish_Datetime'])\n\ncolor = alt.condition(date1_selection, alt.Color('RegionID:N'), alt.value('lightgray'))\n\nchart = alt.Chart(regional_df).mark_rect().encode(\n x='Date',\n y='Availability',\n color='Publish_Datetime',\n opacity=alt.condition(\n (region_selection & (date1_selection | date2_selection)),\n ))\n\nchart"